Our work in progress deals with 1) establishing whether or not outer cell membranes or corpora lutea are exclusive sites for prostaglandin (PG) E1, and F2 alpha and gonadotropin receptors, 2) solubilization and purification of PG and gonadotropin receptors to study their true biochemical nature as well as to raise antibodies to pure receptors, (3) assessing the physiological significance of these receptors by the use of antibodies to receptors and measuring hormone binding and consequences of this interaction in various reproductive states, and (4) establishing quantitative and qualitative relationships between hormone binding nd the consequences of this phenomenon in isolated luteal cells. The question of whether or not PG and gonadotropin receptors are exclusively localized in outer cell membranes is a matter yet to be resolved. The solubilization and purification studies, besides giving information on the true biochemical nature of the receptors, can also easily test the possibilities that PGE, PGF2 alpha, and hCG bind to different sites on the same receptor molecule or bind to different molecules. Raising antibodies to pure receptors and using such specific antibodies in physiological studies would be a novel approach towards understanding several potentially important biological phenomena. It would be an equally novel approach to try and block luteal function at will using receptor specific antibodies. This proposal also takes a look at whether the target tissue responsiveness to PGs and gonadotropins is regulated by the availability of the receptors and/or decrease in efficiency in intramembranous coupling of receptor binding and activation of biological response. In summary, the work in progress attempts to answer some basic questions regarding the mechanism of PGs and gonadotropins action in corpus luteum.